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HomeMy WebLinkAboutWPO202100034 Calculations 2021-10-04VICTORIAN HEIGHTS VSMP STORMWATER MANAGEMENT CALCULATIONS PACKET Date of Calculations October 4, 2021 PREPARED BY: COLLINS ENGI°-°''mRING 200 GARRETT STREET, SUITE K CHARLOTTESVILLE, VA 22902 434.293.3719 PH 434.293.2813 FX www.collins-engineering.com SCS TR-55 Calculations Si " . . !Database) Soils Table (Source: NRCS Web Soil Survey Online Database) Note: The soils' properties witin this development are predominantly composed of hydrologic group type B soils. Albemarle County, Virginia (VA003) Albemarle County, Virginia (VA003) Map Unit Map Unit Name Percent of AOI Symbol 27B Elioak loam, 2 to 7 6.8% percent slopes 27C Elioak loam, 7 to 37.2% 15 percent slopes 39D Hazel loam, 15 to 8.9% 25 percent slopes 65B Fairview sandy 47.2% loam, 2 to 7 percent slopes Totals for Area of 100.00yo Interest Precipitation Data (Source: NOAA's National Weather Service, Hydrometerorological Design Studies Center, Atlas 14 Point Precipitation Frequency Estimates) POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Atlas 14, VOIUtile 2, Version 3 PF tabular PDS-based point precipitation frequency estimates with 90% confidence intervals (in inches)t Average recurrence interval (years) t 2 5 70 25 50 700 200 500 7000 24hr (2.70-3.37) (3.264.08) (4.15-5.21) (/.89b.1/) (5.97-7.52) (6.87-8.70) (7.85-10.0) (8.89-11.4) (10.a13.6) (11.6-15.4) 0-3. 3.63 4.64 5.48 6.-T 7.81 8.-1 10.3 722 .6-1 Map v 0 Tertam a or E 3 0 o a) Select location Move crosshair or double click b) Clkk on stedon icon ❑ Shaw stations on map Location information: South h h„ Name: Charlottesville. Virginia, USA' oe a Latitude: 38.0975° RSoutFork River �'a e Longitude:-78,46850 Reservolr a4�s y Elevation: 500.6 it I 90 O� Ce MFd lip ° u e x P^ ya W o.6e g n r- + 3 R e 200 v g0 4 I--� A Source,-ESRI Maps aWtt s °of "Source: USGS POINT PRECIPITATION FREQUENCY (PF) ESTIMATES WITH 90% CONFIDENCE INTERVALS AND SUPPLEMENTARY INFORMATION NOAA Ada. 14, Volume 2, Version 3 Channel and Flood Protection Calculations U.S. Department of Agriculture Natural Resources Conservation Service Project: Victorian Heights Location: Berkmar Drive Check One: Present X 1. Runoff curve Number (CN) Developed TR 55 Worksheet 2: Runoff Curve Number and Runoff Designed By: LMW, PE Checked By: SRC, PE FL-ENG-21A 06/04 Date: 9/20/2021 Date: 9/20/2021 Cover description CN (weighted) _Calculated Drainage Area Soil name and hydrologic (Cover type, treatment, and hydrologic condition; percent CN Area Product of CN x total product/ 'S' Description group (Appendix A) (Acres) Area Value impervious; unconnected/ connected impervious area ratio) total area Impervious Areas 98 0.21 20.6 DAA B Lawns in Good Condition (25%+/-) 61 0.29 17.7 62 6.13 (Pre-Dev.) Woods Grass Good Condition 58 1.81 105.0 Impervious Areas 98 0.14 13.7 DAB B Lawns in Good Condition (25%+/-) 61 0.50 30.5 60 6.54 (Pre-Dev.) Woods Grass Good Condition 58 1 2.26 131.1 Impervious Areas 98 3.02 295.6 DAA (Post-Dev) B Lawns in Good Condition 61 1.54 93.9 85 1.70 Woods Grass Good Condition SS 0.00 0.0 DAC Impervious Areas 98 0.08 7.8 (Post-Dev) B Lawns in Good Condition 61 0.57 34.8 66 5.25 Woods Grass Good Condition 58 0.00 0.0 2. Runoff 1-Year Storm 2-Year Storm 10-Year Storm Drainage Area Description Frequency -years 1 2 10 n/a Rainfall, P (24 hour)- inches 3.00 3.63 5.48 n/a Runoff, Q-inches 0.40 0.68 1.74 DA A(Pre-Dev.) Runoff, Q-inches 0.35 0.61 1.62 DA B(Pre-Dev) Runoff, Q-inches 1.62 2.17 3.86 DA A(Post-Dev) Runoff, Q- inches 0.53 0.85 2.03 DA C(Post-Dev) TR 55 Worksheet 3: Time of Concentration (TJ or Travel Time (T,) Project: Victorian Heights Location: Berkmar Drive Check One: Present X Developed Check One: T, X T, Sheet Flow: (Applicable to Tc only) X Segment ID: 1 Surface description (Table 3-1) 2 Manning's roughness coeff., n (Table 3-1) 3 Flow length, L (total L < 100) (ft) 4 Two-year 24-hour rainfall, Pz (in.) 5 Land slope, s (ft/ft) 6 Compute T, _ [0.007(n•L)"] / P20.5 s A Shallow Concentrated Flow: 7 Surface description (paved or unpaved) 8 Flow Length, L (ft) 9 Watercourse slope, s (ft/ft) 10 Average velocity, V (Figure 3-1) (ft/s) 11 T, = L / 3600-V Channel Flow: 12 Cross sectional flow area, a (ft) 13 Wetted perimeter, P. (ft) 14 Hydraulic radius, r = a/Pw (ft) 15 Channel Slope, s (ft/ft) 16 Manning's Roughness Coeff, n 17V=[1.49r"'s°5]/n 18 Flow length, L (ft) 19 T,= L / 3600'V 20 Watershed or subarea T, or T, (Add T, in steps 6, 11 and 19) Designed By: Checked By: n/a Date: 9/20/2021 Date: 9/20/2021 DA A DA B DA A DA C (Pre-Dev.) (Pre-Dev.) (Post-Dev) (Post-Dev) Smooth Smooth Smooth Smooth Surface Surface Surface Surface 0.011 0.011 0.011 0.011 15 25 100 45 3.63 3.63 3.63 3.63 0.02 0.02 0.01 0.09 0.00 0.01 0.03 0.01 Unpaved Unpaved Paved Paved 400 265 161 73 0.08 0.17 0.01 0.01 4.6 6.5 1.3 2.3 0.02 0.01 0.03 0.01 ON 0.10 0.10 0.10 0.10 U.S. Department of Agriculture Natural Resources Conservation Service Project: Location: Check One: Victorian Heights Berkmar Drive Present X Developed X TR 55 Graphical Peak Discharge Method Date: 9/20/2021 Date: 9/20/2021 1. Data Drainage Area Description Drainage Area Description Drainage Area Description Drainage Area Description DAA (Pre-Dev.) DAB (Pre-Dev.) DAA (Post-Dev) DAC (Post-Dev) Drainage Area (Am) in miles = 0.0036 0.0045 0.0081 0.0010 Runoff curve number CN= 62 60 85 66 Time of concentration (Tc)= 0.10 0.10 0.20 0.10 Rainfall distribution type= Type II Type II Type II Type II Pond and swamp areas spread throughout the watershed= 0 0 0 0 2. Frequency -years 1 2 10 1 2 10 1 2 10 1 2 10 3. Rainfall, P (24 hour)- inches 3.00 3.63 5.48 3.00 3.63 5.48 3.00 3.63 5.48 3.00 3.63 5.48 4. Initial Abstraction, la- inches 1.23 1.23 1.23 1.31 1.31 1.31 0.35 0.35 0.35 1.03 1.03 1.03 5. Compute la/P 0.41 0.34 0.22 0.44 0.36 0.24 0.12 0.10 0.06 0.34 0.28 0.19 6. Unit peak discharge, Qu- csm/in Out of Range. Hydrograph for See Flows Out of Range. Hydrograph for See Flows Out of Range. See Hydrograph for Flows Out of Range. See Hydrograph for Flows 7. Runoff, Qfrom Worksheet 2- inches 0.40 0.68 1.74 0.35 0.61 1.62 1.62 2.17 3.86 0.53 0.85 2.03 8. Pond and Swamp adjustment factor, Fp 1 1 1 1 1 1 1 1 1 1 1 1 9. Peak Discharge, Qp- cfs where Qp=Qu Am Q Fp 1.15 F22F611 1.22 2.42 7.10 Routed through Underground Detention Basin 1 1 0.42 0.81 2.01 WATERSHED SUMMARY CN Area, 1-year Flow, 2-year Flow, 10-year Flow, ac. cfs cfs cfs DAA+B(Pre-Dev) 61 5.21 2.37 4.65 13.21 Area, 1-year Flow, 2-year Flow, 10-year Flow, CN ac. cfs cfs cfs DA A + C (Post-Dev) 83 5.21 0.50 1.14 12.51 9 VAC 25-870-66 Section B: Channel Protection Utilizing a 1-inch Orifice "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet the criteria in subdivision 1, 2 or 3 of this subsection..." Section B.1: Manmade stormwater conveyance systems "When stormwater from a development is discharged to a manmade stormwater conveyance system, following the land -disturbing activity, either..." a. or b. shall be met: Section B.l.b. "The peak discharge requirements for concentrated stormwater flow to natural stormwater conveyance systems in subdivision 3 of this subsection shall be met." Section 8.3 "... the maximum peak flow rate from the one-year 24-hour storm following the land -disturbing activity shall be calculated either.." a. or b." Section 6.3.a. In accordance with the following methodology: Q Allowed < I.F. * (Q Pr�Developed + (RV Pre -Developed) ) I (RV Developed ) Q Allowed < 0.50 cfs Where: QPre-Developed= 2.37cfs (FromTR-55) CN Pr�Developed= 61 (From Curve Number Summary) S Pre -Developed = 6.29 (From SCS TR-55 eq. 2-4) RV Pr�Developed= 0.38 in. (From SCSTR-55 eq. 2-3) CN Pt -Developed= 83 (From Curve Number Summary) S P.A Developed = 2.05 (From SCS TR-55 eq. 2-4) RV port -Developed= 1.45 in. (From SCS TR-55 eq. 2-3) I.F. = 0.80 (Factor of Safety) Q Developed = 0.50 cfs Section B.4 Limits of Analysis The analysis terminates at Post -Development Subarea A+C since subsection B.3.a is met. 9 VAC 25-870-66 Section C: Flood Protection "Concentrated stormwater flow shall be released into a stormwater conveyance system and shall meet one of the following criteria as demonstrated by use of acceptable hydrologic and hydraulic methodologies:" Section C.2.b.: The point of discharge (Detention Basin B's Cutfall), "releases a postdevelopment peak flow rate for the 10-year 24-hour storm event that is less than the predevelopment peak flow rate from the 10-year 24-hour storm event. Downstream stormwater conveyance systems do not require any additional analysis to show compliance with flood protection criteria if this option is utilized." 10-Year, 24-Hour Pre -Development Subareas A & B Peak Flow Rate = 13.21 cfs 10-Year, 24-Hour Post -Development Subarea A & C Peak Flow Rate = 12.51 cfs Section C.3 Limits of Analysis The flood protection analysis terminates at Subarea A+C since subsection C.2.b is met. Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in) DA A 0.10 0.10 0.41 0.0014 (Pre-Dev.) Hydrograph Time (hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.10 12.0 0.42 12.1 1.15 12.2 0.64 12.3 0.30 12.4 0.25 12.5 0.22 12.6 0.19 12.7 0.16 12.8 0.15 13.0 0.13 13.2 0.12 13.4 0.11 13.6 0.10 13.8 0.09 14.0 0.09 14.3 0.08 14.6 0.08 15.0 0.07 15.5 0.06 16.0 0.06 16.5 0.05 17.0 0.05 17.5 0.05 18.0 0.05 19.0 0.04 20.0 0.04 22.0 0.03 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A) Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA A 0.10 0.10 0.34 0.0024 (Pre-Dev.) Hydrograph Time (hrs.) 2-yr Discharge s (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.28 12.0 1.09 12.1 2.23 12.2 1.19 12.3 0.52 12.4 0.42 12.5 0.37 12.6 0.31 12.7 0.27 12.8 0.24 13.0 0.22 13.2 0.19 13.4 0.18 13.6 0.16 13.8 0.15 14.0 0.14 14.3 0.13 14.6 0.12 15.0 0.11 15.5 0.10 16.0 0.09 16.5 0.08 17.0 0.08 17.5 0.08 18.0 0.07 19.0 0.06 20.0 0.06 22.0 0.05 26.0 0.00 4 0 SCS TR-SS Pre-ReDevelopment Unit Hydrograph (ON DA A) 0 5 10 15 20 25 30 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in) DA A 0.10 0.10 0.22 0.0063 (Pre-Dev.) Hydrograph Time (hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.06 11.3 0.09 11.6 0.13 11.9 1.42 12.0 3.77 12.1 6.11 12.2 3.55 12.3 1.37 12.4 1.02 12.5 0.87 12.6 0.74 12.7 0.62 12.8 0.56 13.0 0.49 13.2 0.43 13.4 0.39 13.6 0.35 13.8 0.32 14.0 0.30 14.3 0.27 14.6 0.25 15.0 0.23 15.5 0.21 16.0 0.19 16.5 0.17 17.0 0.16 17.5 0.15 18.0 0.15 19.0 0.13 20.0 0.11 22.0 0.10 26.0 0.00 6 s a 3 2 1 0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A) Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am'Q (miz-in) DA B 0.10 0.10 0.44 0.0016 (Pre-Dev.) Hydrograph Time (hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.07 12.0 0.35 12.1 1.22 12.2 0.66 12.3 0.32 12.4 0.27 12.5 0.24 12.6 0.21 12.7 0.18 12.8 0.16 13.0 0.15 13.2 0.13 13.4 0.12 13.6 0.11 13.8 0.11 14.0 0.10 14.3 0.09 14.6 0.09 15.0 0.08 15.5 0.07 16.0 0.07 16.5 0.06 17.0 0.06 17.5 0.06 18.0 0.05 19.0 0.05 20.0 0.04 22.0 0.04 26.0 0.00 6 5 a 3 2 1 03 SCS TR-55 Pre -Re Development Unit Hydrograph (ON DA B) 0 5 10 15 20 25 30 Worksheet Sb (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA B 0.10 0.10 0.36 0.0028 (Pre-Dev.) Hydrograph Time (hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.32 12.0 1.22 12.1 2.42 12.2 1.34 12.3 0.58 12.4 0.47 12.5 0.41 12.6 0.35 12.7 0.30 12.8 0.27 13.0 0.25 13.2 0.22 13.4 0.20 13.6 0.18 13.8 0.17 14.0 0.16 14.3 0.14 14.6 0.14 15.0 0.13 15.5 0.11 16.0 0.10 16.5 0.09 17.0 0.09 17.5 0.09 18.0 0.08 19.0 0.07 20.0 0.06 22.0 0.06 26.0 0.00 6 5 4 3 2 1 31 SCS TR-55 Pre -Re Development Unit Hydrograph (ON DA B) 0 5 30 15 20 25 30 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA B 0.10 0.10 0.24 0.0074 (Pre-Dev.) Hydrograph Time (hrs.) 1-yr Discharge s (cfs) 0.0 0.00 11.0 0.05 11.3 0.08 11.6 0.12 11.9 1.53 12.0 4.35 12.1 7.10 12.2 4.07 12.3 1.60 12.4 1.21 12.5 1.04 12.6 0.88 12.7 0.74 12.8 0.67 13.0 0.59 13.2 0.52 13.4 0.47 13.6 0.43 13.8 0.39 14.0 0.36 14.3 0.32 14.6 0.31 15.0 0.28 15.5 0.25 16.0 0.23 16.5 0.21 17.0 0.20 17.5 0.19 18.0 0.18 19.0 0.16 20.0 0.13 22.0 0.12 26.0 0.00 4 0 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA B) 0 5 10 is 20 25 30 Post -Development Detention Basin Routings and Outflow Hydrographs The following routing calculations and outflow hydrographs reflect the post -development attenuation in Subarea A from the proposed underground detention facility. Post -Development DA A Inflow Hydrograph 0.0 0.00 0.5 0.07 1.0 0.08 1.5 0.08 2.0 0.09 2.5 0.09 3.0 0.10 3.5 0.10 4.0 0.10 4.5 0.11 5.0 0.12 5.5 0.12 6.0 0.13 6.5 0.13 7.0 0.15 7.5 0.15 8.0 0.16 8.5 0.19 9.0 0.23 9.5 0.23 10.0 0.28 10.5 0.37 11.0 0.51 11.3 0.69 11.6 1.61 11.9 9.19 12.0 3.96 12.1 2.44 12.2 1.32 12.3 1.08 12.4 0.92 12.5 0.75 12.6 0.63 12.7 0.59 12.8 0.55 13.0 0.47 13.2 0.41 13.4 0.38 13.6 0.34 13.8 0.31 14.0 0.28 14.3 0.26 14.6 0.24 15.0 0.22 15.5 0.20 16.0 0.17 16.5 0.16 17.0 0.15 17.5 0.15 18.0 0.13 19.0 0.11 20.0 0.10 22.0 0.09 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 10.00 8.00 6.00 4.00 2.00 0.00 -2.00 Inflow Hydrograph (1-yr Design Storm) 1.0 Post -Development DA A Inflow Hydrograph 0.0 0.00 0.5 0.10 1.0 0.11 1.5 0.11 2.0 0.12 2.5 0.12 3.0 0.13 3.5 0.13 4.0 0.14 4.5 0.15 5.0 0.16 5.5 0.16 6.0 0.18 6.5 0.18 7.0 0.20 7.5 0.21 8.0 0.22 8.5 0.26 9.0 0.31 9.5 0.31 10.0 0.38 10.5 0.49 11.0 0.68 11.3 0.92 11.6 2.16 11.9 12.33 12.0 9.81 12.1 3.27 12.2 1.78 12.3 1.45 12.4 1.23 12.5 1.00 12.6 0.85 12.7 0.79 12.8 0.73 13.0 0.63 13.2 0.56 13.4 0.51 13.6 0.45 13.8 0.42 14.0 0.38 14.3 0.34 14.6 0.33 15.0 0.30 15.5 0.26 16.0 0.23 16.5 0.22 17.0 0.21 17.5 0.19 18.0 0.18 19.0 0.15 20.0 0.13 22.0 0.12 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 14.00 12.00 10.00 8.00 6.00 4.00 2.00 0.00 -2.00 Inflow Hydrograph (2-yr Design Storm) 1.0 Past -Development DA A Inflow Hydrograph 0.0 0.00 0.5 0.18 1.0 0.19 1.5 0.20 2.0 0.21 2.5 0.21 3.0 0.23 3.5 0.23 4.0 0.25 4.5 0.26 5.0 0.28 5.5 0.28 6.0 0.32 6.5 0.32 7.0 0.35 7.5 0.37 8.0 0.39 8.5 0.46 9.0 0.55 9.5 0.56 10.0 0.68 10.5 0.89 11.0 1.22 11.3 1.65 11.6 3.86 11.9 22.07 12.0 19.77 12.1 5.86 12.2 3.18 12.3 2.60 12.4 2.21 12.5 1.80 12.6 1.52 12.7 1.42 12.8 1.32 13.0 1.14 13.2 1.00 13.4 0.92 13.6 0.81 13.8 0.74 14.0 0.67 14.3 0.62 14.6 0.58 15.0 0.53 15.5 0.47 16.0 0.41 16.5 0.39 17.0 0.37 17.5 0.35 18.0 0.32 19.0 0.27 20.0 0.23 22.0 0.21 26.0 0.00 26.5 0.00 27.0 0.00 27.5 0.00 25.00 20.00 15.00 10.00 5.00 0.00 -5.00 Inflow Hydrograph (10-yr Design Storm) 1.0 BasinFlow printout INPUT: Basin: 0 Contour Areas Elevation(ft) Area(sf) Computed Vol.(cy) 3 Storage Pipes Storage pipe 0 name: name diameter (in) 120.000 length (ft) 133.000 invert (ft) 507.565 angle 0.287 volume (cy) 386.881 Storage pipe 1 name: name diameter (in) 120.000 length (ft) 146.000 invert (ft) 507.500 angle 0.287 volume (cy) 424.697 Storage pipe 2 name: name diameter (in) 120.000 length (ft) 133.000 invert (ft) 507.500 angle 0.287 volume (cy) 386.881 Start—Elevation(ft) 507.50 Vol.(cy) 5 Outlet Structures Outlet structure 0 Orifice name: BARREL area (sf) 1.227 diameter or depth (in) 15.000 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 507.400 multiple 1 discharge out of riser Outlet structure 1 Orifice name: LOW-RISE ORIFICE area (sf) 0.008 diameter or depth (in) 1.200 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 507.500 multiple 1 discharge into riser Outlet structure 2 Orifice name: EMERGENCY BYPASS PIPE area diameter or depth width for rect. coeffi invert mul discharge Outlet structure 3 Orifice (sf) 1.227 (in) 15.000 (in) 0.000 -ient 0.600 (ft) 516.000 tiple 1 out of riser name: MID -RISE ORIFICE area (sf) 1.375 diameter or depth (in) 11.000 width for rect. (in) 18.000 coefficient 0.600 invert (ft) 514.100 multiple 1 discharge into riser Outlet structure 4 Orifice name: OVERFLOW WEIR area (sf) 0.520 diameter or depth (in) 9.760 width for rect. (in) 0.000 coefficient 0.600 invert (ft) 517.250 multiple 1 discharge into riser 3 Inflow Hydrographs Hydrograph 0 SCS name: 1 YR Area (acres) 4.560 CN 85.000 Type 2 rainfall, P (in) 3.000 time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) Hydrograph 1 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) Hydrograph 2 SCS name: Area (acres) CN Type rainfall, P (in) time of conc. (hrs) time increment (hrs) time limit (hrs) fudge factor routed peak flow (cfs) peak time (hrs) volume (cy) OUTPUT: 2 10 YR 2 0.1000 0.0200 30.000 1.00 true 9.190 11.917 972.944 3.630 0.1000 0.0200 30.000 1.00 true 12.325 11.917 1304.834 5.480 0.1000 0.0200 30.000 1.00 true 22.070 11.917 2336.569 Routing Method: storage -indication Hydrograph 0 Routing Summary of Peaks: 1 YR inflow (cfs) 9.147 at discharge (cfs) 0.096 at water level (ft) 513.955 at 11.92 (hrs) 18.38 (hrs) 19.98 (hrs) storage (cy) 763.942 Hydrograph 1 Routing Summary of Peaks: 2 YR inflow (cfs) 12.267 at 11.92 (hrs) discharge (cfs) 1.010 at 12.48 (hrs) water level (ft) 514.445 at 12.48 (hrs) storage (cy) 835.887 Hydrograph 2 Routing Summary of Peaks: 10 YR inflow (cfs) 21.967 at 11.92 (hrs) discharge (cfs) 10.994 at 12.04 (hrs) water level (ft) 517.259 at 12.04 (hrs) storage (cy) 1167.443 Mon Oct 04 14:53:11 EDT 2021 Post -Development Site Outflow Hydrographs The following outflow hydrographs reflect the post -development outflow from the site by adding the hydrographs for Subarea A (from detention routings) and Subarea C (undetained). Post -Development DA A Outflow Hydrograph (From Underground Detention Routings) Time (hrs) Outflow (cfs) 0.0 0.00 11.0 0.06 11.3 0.06 11.6 0.06 11.9 0.08 12.0 0.08 12.1 0.09 12.2 0.09 12.3 0.09 12.4 0.09 12.5 0.09 12.6 0.09 12.7 0.09 12.8 0.09 13.0 0.09 13.2 0.09 13.4 0.09 13.6 0.09 13.8 0.09 14.0 0.09 14.3 0.09 14.6 0.09 15.0 0.09 15.5 0.09 16.0 0.10 16.5 0.10 17.0 0.10 17.5 0.10 18.0 0.10 19.0 0.10 20.0 0.10 22.0 0.10 26.0 0.09 27.0 0.09 30.0 0.06 Outflow Hydrograph (1-yr Design Storm) 0.12 0.10 0.08 0.06 0.04 0.02 0.00 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 Post -Development DA A Outflow Hydrograph (From Underground Detention Routings) Time (hrs) Outflow (cfs) 0.0 0.00 11.0 0.06 11.3 0.07 11.6 0.07 11.9 0.09 12.0 0.09 12.1 0.17 12.2 0.58 12.3 0.84 12.4 0.98 12.5 1.01 12.6 0.98 12.7 0.92 12.8 0.86 13.0 0.74 13.2 0.64 13.4 0.55 13.6 0.48 13.8 0.42 14.0 0.37 14.3 0.31 14.6 0.27 15.0 0.23 15.5 0.20 16.0 0.17 16.5 0.15 17.0 0.14 17.5 0.12 18.0 0.12 19.0 0.10 20.0 0.10 22.0 0.10 26.0 0.10 27.0 0.10 30.0 0.09 1.20 1.00 0.80 0.60 0.40 0.20 0.00 Outflow Hydrograph (2-yr Design Storm) 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 Post -Development DA A Outflow Hydrograph (From Underground Detention Routings) Time (hrs) Outflow (cfs) 0.0 0.00 11.0 0.08 11.3 0.08 11.6 0.09 11.9 6.84 12.0 10.40 12.1 10.99 12.2 8.78 12.3 7.18 12.4 5.74 12.5 4.43 12.6 2.65 12.7 2.08 12.8 1.75 13.0 1.37 13.2 1.17 13.4 1.05 13.6 0.94 13.8 0.83 14.0 0.74 14.3 0.63 14.6 0.56 15.0 0.49 15.5 0.42 16.0 0.36 16.5 0.31 17.0 0.28 17.5 0.26 18.0 0.24 19.0 0.20 20.0 0.16 22.0 0.13 26.0 0.10 27.0 0.10 30.0 0.09 12.00 10.00 8.00 6.00 4.00 2.00 0.00 -2.00 Outflow Hydrograph (10-yr Design Storm) 1.0 Worksheet 5b (Modified for Clarity): Basic watershed Data 1-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA C 0.10 0.10 0.34 0.0005 (Post-Dev) Hydrograph Time (hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.06 12.0 0.22 12.1 0.42 12.2 0.24 12.3 0.11 12.4 0.09 12.5 0.08 12.6 0.06 12.7 0.05 12.8 0.05 13.0 0.04 13.2 0.04 13.4 0.04 13.6 0.03 13.8 0.03 14.0 0.03 14.3 0.03 14.6 0.02 15.0 0.02 15.5 0.02 16.0 0.02 16.5 0.02 17.0 0.02 17.5 0.02 18.0 0.01 19.0 0.01 20.0 0.01 22.0 0.01 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA C) Worksheet 5b (Modified for Clarity): Basic watershed Data 2-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA C 0.10 0.10 0.28 0.0009 (Post-Dev) Hydrograph Time (hrs.) 2-yr Discharge s (cfs) 0.0 0.00 11.0 0.00 11.3 0.00 11.6 0.00 11.9 0.14 12.0 0.49 12.1 0.81 12.2 0.46 12.3 0.19 12.4 0.15 12.5 0.13 12.6 0.11 12.7 0.09 12.8 0.08 13.0 0.07 13.2 0.06 13.4 0.06 13.6 0.05 13.8 0.05 14.0 0.05 14.3 0.04 14.6 0.04 15.0 0.04 15.5 0.03 16.0 0.03 16.5 0.03 17.0 0.03 17.5 0.02 18.0 0.02 19.0 0.02 20.0 0.02 22.0 0.02 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA Q 30 Worksheet 5b (Modified for Clarity): Basic watershed Data 10-yr. 24-hr. SCS TR-55 Method Unit Hydrograph for the la/P & Tc Listed Below Subarea Tc (hrs.) Tt (hr.) la / P Am*Q (miz-in) DA C 0.10 0.10 0.19 0.0021 (Post-Dev) Hydrograph Time 10-yr (hrs.) Discharges (cfs) 0.0 0.00 11.0 0.03 11.3 0.04 11.6 0.06 11.9 0.52 12.0 1.26 12.1 2.01 12.2 1.19 12.3 0.45 12.4 0.33 12.5 0.28 12.6 0.23 12.7 0.20 12.8 0.18 13.0 0.15 13.2 0.13 13.4 0.12 13.6 0.11 13.8 0.10 14.0 0.09 14.3 0.08 14.6 0.08 15.0 0.07 15.5 0.06 16.0 0.06 16.5 0.05 17.0 0.05 17.5 0.05 18.0 0.05 19.0 0.04 20.0 0.03 22.0 0.03 26.0 0.00 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA C) Site Outflow (DA A + DA C) Hydrograph Time (hrs.) 1-yr Discharges (cfs) 0.0 0.00 11.0 0.06 11.3 0.06 11.6 0.06 11.9 0.13 12.0 0.30 12.1 0.50 12.2 0.33 12.3 0.19 12.4 0.17 12.5 0.16 12.6 0.15 12.7 0.14 12.8 0.14 13.0 0.14 13.2 0.13 13.4 0.13 13.6 0.13 13.8 0.12 14.0 0.12 14.3 0.12 14.6 0.12 15.0 0.12 15.5 0.11 16.0 0.11 16.5 0.11 17.0 0.11 17.5 0.11 18.0 0.11 19.0 0.11 20.0 0.11 22.0 0.11 26.0 0.09 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.0 SCS TR-55 Post-ReDevelopment Unit Hydrograph (ON DA A+C) 5.0 10.0 15.0 20.0 25.0 30.0 Site Outflow (DA A + DA Q Hydrograph Time (hrs.) 2-yr Discharges (cfs) 0.0 0.00 11.0 0.07 11.3 0.07 11.6 0.07 11.9 0.23 12.0 0.59 12.1 0.98 12.2 1.04 12.3 1.03 12.4 1.12 12.5 1.14 12.6 1.08 12.7 1.01 12.8 0.94 13.0 0.81 13.2 0.70 13.4 0.61 13.6 0.53 13.8 0.47 14.0 0.41 14.3 0.35 14.6 0.31 15.0 0.27 15.5 0.23 16.0 0.20 16.5 0.17 17.0 0.16 17.5 0.15 18.0 0.14 19.0 0.12 20.0 0.11 22.0 0.11 26.0 0.10 1.20 1.00 0.80 0.60 0.40 0.20 SCS TR-55 Post-ReDevelopment Unit Hydrograph (ON DA A+C) 5.0 MD 15.0 20.0 25.0 30.0 Site Outflow (DA A+ DA Q Hydrograph Time (hrs.) 10-yr Discharges (cfs) 0.0 0.00 11.0 0.11 11.3 0.12 11.6 0.15 11.9 7.36 12.0 12.25 12.1 12.51 12.2 9.97 12.3 7.62 12.4 6.07 12.5 4.70 12.6 2.89 12.7 2.28 12.8 1.92 13.0 1.52 13.2 1.31 13.4 1.17 13.6 1.05 13.8 0.93 14.0 0.83 14.3 0.72 14.6 0.64 15.0 0.56 15.5 0.48 16.0 0.42 16.5 0.36 17.0 0.33 17.5 0.30 18.0 0.28 19.0 0.24 20.0 0.19 22.0 0.16 26.0 0.10 SCS TR-55 Pre-ReDevelopment Unit Hydrograph (ON DA A+C) e 5 4 3 2 1 0 0 5 10 15 20 25 30 Virginia Runoff Reduction Method Water Quality Calculations (COMPLIANCE IS MET THROUGH THE BEST MANAGEMENT PRACTICE OF PURCHASING NUTRIENT CREDITS. 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D.A.E ARMECK FOREST/OVEN SPACE (a[) am O.W 0.00 i0.00 O.W OK. IMPERWOUS MVER (ac) IMPERVnMCOVERTRENTFD)ac) am 0.00 0.00 0.00 0.00 0.00�M. 0.00 OWOK. OK.. MANAGEDTURFAREA(a[) 0.00 O.00 0.00 00.W OK. MANAGED TURF AREA TREATED(a[) am O.00 0.00 0.00 OK. AREA CHECK OK OK. OK. OK. Site Treatment VOIUme (ffa) 11.191 Runoff Reduction Volume and TP By Drainage Area O.A. A O.A. C D.AD O.A. E TOTALRUNOFF REDUMM VOLUME ACHIEVED pF) 0 0 0 00 AL Qb/1) LOADAVAKABLE FNhh 0.00 MAI 0.00 0.000.0.00 TPIDADREOUCTIED pb/yr) 0.00 0.00 0.00 O.W am TP LOADNG )Ib/yr) 0.00 0.00 0.00 O.W am NMWGEN IDAD REDUCTIEDpb/yr) am O.W 0.00 0.00 O.W 0.00 Totphorus FINAL POST-DEVELOPMAD Qb/yr)WTPLOADREDUCTIED pb/yr�TPIDADREOUCTIED pb/yr)W LOADREMAINING Qb/,): REMAINING TP LOAD REDUCTION REQUIRED (lb/yr): 5.56